Field of the Invention
The present invention relates to a technology for refining a structure by using a restraint.
Description of the Related Art
In analysis of a crystal structure, there are cases where a method of specifying a crystal structure model which best fits measurement data by using the method of least squares is adopted. If measurement data of low quality is used in such a method, a result which is not chemically reasonable may be obtained in some cases. However, it is possible to cope with this situation by setting weak constraint conditions (restraints) on an interatomic bond distance and an interatomic bond angle (see Jurg Waser, “Least-Squares Refinement with Subsidiary Conditions”, Acta Cryst, 1963, Vol. 16, P1091).
However, if the set restraint is too strong, analysis that the measurement data has been disregarded may be obtained. Setting of the restraint has been performed on the basis of individual judgment so far (see Attilio Immirzi, “Constraints and restraints in crystal structure Analysis”, Journal of Applied Crystallography, 2009, Vol. 42, P362-364). For example, setting of the restraint may be performed intensely in order to perform analysis that importance has been attached to a chemically reasonable crystal structure in some cases. In addition, the restraint may be set such that the bond distance and bond angle which are remarkably different from those of a known crystal structure which is partially similar to the crystal structure concerned have reasonable values in other cases.
If the intensity of the restraint in structure refinement is adjusted on the basis of individual decision as mentioned above, it may sometimes occur that the chemically reasonable crystal structure is not obtained and/or analysis that the measurement data has been disregarded is performed. Absence of an index for appropriate restraint intensity may be one of the causes of occurrence of such situations.